It is possible that the main title of the report Marfan Syndrome is not the name you expected. Please check the synonyms listing to find the alternate name(s) and disorder subdivision(s) covered by this report.
As Jenny points out, being able to lisp the alphabet song at age two has little to do with 'knowing' the alphabet. And, yes, most children learn the letters by sight and sound in kindergarten, although most are capable of learning this information sooner if diligently taught by parents or others.
Simply concentrate on a few letters at a time and allow your child to see, hear, and experience that letter in a variety of ways. Remember that children learn by utilizing their senses so while alphabet books can be a helpful learning tool you should utilize a number of approaches to teach the ABCs. Buy or make letters that children can experience in 3-D and let the child construct letters as well using play dough.